2021 Fiscal Year Final Research Report
Real form of the cap structure of volcanic hydrothermal system and estimate of permeability
| Project/Area Number |
18K03777
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 17040:Solid earth sciences-related
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
Kanda Wataru 東京工業大学, 理学院, 准教授 (00301755)
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| Co-Investigator(Kenkyū-buntansha) |
高倉 伸一 国立研究開発法人産業技術総合研究所, 地質調査総合センター, 上級主任研究員 (50357349)
丹保 俊哉 公益財団法人立山カルデラ砂防博物館, 学芸課, 学芸課長補佐 (10574311)
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| Project Period (FY) |
2018-04-01 – 2022-03-31
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| Keywords | 比抵抗構造 / 透水係数 / 浸透率 / 水蒸気噴火 / 変質鉱物 |
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| Outline of Final Research Achievements |
To clarify the subsurface structure of the volcanic hydrothermal system in a highly acidic environment, we constructed a flow experiment column device and tried to measure the electrical resistivity and the hydraulic conductivity simultaneously, but we could not obtain sufficient measurement results.
In Tateyama Jigokudani, where the detailed resistivity structure was estimated, the distribution of soil diffuse CO2 flux and the hydraulic conductivity of the soil were measured, and the chemical analysis of the soil was performed. As a result, although the surface layer in the central part of Jigokudani is not as low in permeability as the clay layer in the peripheral part, we found that the hydraulic conductivity is reduced by silica minerals and sulfate minerals. Although the direct relationship between resistivity and permeability was not obtained, it is concluded that the low resistivity of the surface layer is caused by highly acidic fluids containing a large amount of ions.
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| Free Research Field |
火山電磁気学
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| Academic Significance and Societal Importance of the Research Achievements |
水蒸気噴火の発生場と考えられている火山熱水系キャップ構造は、低浸透率かつ低比抵抗のキャップロックとその下部の流体溜りから形成されていると考えられているが、強酸性環境下にある火口や噴気地帯直下では、その実体は必ずしも明らかではなかった。本研究により、透水性を低下させている物質はシリカ鉱物や硫黄および硫酸塩鉱物であり、低比抵抗を担っている物質は強酸性の熱水であることが確認できた。従来の低比抵抗かつ低浸透率の粘土によるキャップが形成されているとする比抵抗構造の解釈を覆すものであり、水蒸気噴火発生場の理解が進展するものと期待できる。
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